How do I determine the efficiency of heat exchanger?
How do I determine the efficiency of heat exchanger?
(OP)
Hi,
I am trying to figure out how much improvement in the HX efficiency after chemical-cleaned the water tube. It's steam-water HX. Any thoughts?
Thanks in advance
I am trying to figure out how much improvement in the HX efficiency after chemical-cleaned the water tube. It's steam-water HX. Any thoughts?
Thanks in advance





RE: How do I determine the efficiency of heat exchanger?
RE: How do I determine the efficiency of heat exchanger?
RE: How do I determine the efficiency of heat exchanger?
I asssume the steam is condensing at a saturation temperature Ts, based on the pressure of the steam side of the Hx, Ps. This means the governing fluid is the air.
Effectiveness =e= (Tao-Tai)/ (Ts-Tai)
Since the ratio of heat capcities is almost infinite for the case of a condensing fluid ,the effectivness can also be directly calculated by :
e= 1-exp(NTU), where NTU= U*A/(Wa*Cp,a)
where U= overall effective heat transfer coefficient, including effects of fouling and flow maldistribution.
If you measure the e using test data fromthe first equation, you can work bakwrds to the effet overall heat transfer coeficient U, and see how this had improved by the cleaning operation.
RE: How do I determine the efficiency of heat exchanger?
At both opportunities, when taking the unit out for cleaning, and after the chemical cleaning is finished, but before it is returned to duty, run the exchanger with water in such a manner that constant -known- flow rates can be obtained. There are simple methods to measure water flow rates which do not require the installation of instrumentation. If it isn't worth or otherwise desirable to throw away water to drain, collect it for reuse.
Measure temperatures. Compare duties. Estimate efficiencies.
BTW, such an experiment can be done with various water flowrates, to create an ample set of data for comparison.
Please comment.
RE: How do I determine the efficiency of heat exchanger?
The heat transfer is Q=UA.DTlm
and U=(1/ho+1/hio+wall resistance+fouling factors)^-1
For steam on the shell side the ho is 6000 to 800 W/m2K, including fouling factor. Wall resistance and hio will be the same for clean and dirty.
Cleaning will remove the tubeside fouling factor. Lists of fouling factors are given in various chem eng books.
The method of control needs to be considered because if it is a control valve on the condensate side then the HE will be flooded hence reducing the effective heat transfer surface area.
RE: How do I determine the efficiency of heat exchanger?